The invention relates to a pyrotechnical drive for a safety device such as a tensioning device of a safety belt etc. It includes a drive element movable within a guide tube and a gas generator positioned within a receiving member attached to the guide tube. The gas generator is activatable under certain conditions for generating a gas that acts on the drive element in order to move it within the guide tube.
A pyrotechnical drive device with the aforementioned features is, for example, known from German Patent 39 03 148. Such drive devices are especially used for tensioning devices of safety belts which act on the safety belt itself or effect a tensioning movement of an anchoring part for a safety belt lock or act with a suitable coupling onto the safety belt reeling shaft of a coordinated safety belt reeling device. In the aforementioned German Patent 39 03 148 the drive device for a tensioning device acts on the safety belt reeling shaft. The known drive device comprises at one end thereof a cylinder as a receiving member for receiving the gas generator. The gas generator in case of activation releases the gas that drives a piston arranged within the cylindrical guide tube. The piston acts as the drive element.
The aforementioned drive device has the disadvantage that when the piston jams within the guide tube, excessive pressure will build up in the portion of the guide tube positioned between the piston and the gas generator. This may result in a destruction of the guide tube, respectively, of the receiving member for the gas generator and may result in detachment and ejection of parts at the location of rupture.
It is therefore an object of the present invention to improve a drive device of the aforementioned kind such that an effective pressure relief valve is provided that can be manufactured easily.